Black-red-gold is the official flag of the Federal Republic of Germany. As an official symbol of the constitutional order, it is protected against defamation. According to §90 of the German penal code, the consequences are a fine or imprisonment up to five years.
The German association with the colors black, red, and gold surfaced in the radical 1840s, when the black-red-gold flag was used to symbolize the movement against the Conservative European Order that was established after Napoleon’s defeat.
There are many theories in circulation regarding the origins of the color scheme used in the 1848 flag. It has been proposed that the colors were those of the Jena Students’ League (Jenaer Burschenschaft), one of the radically minded Burschenschaften banned by Metternich in the Carlsbad Decrees; the colors are mentioned in their canonical order in the seventh verse of August Daniel von Binzer’s student song Zur Auflösung der Jenaer Burschenschaft (“On the Dissolution of the Jena Students’ League”) quoted by Johannes Brahms in his Academic Festival Overture. Another claim goes back to the uniforms (mainly black with red facings and gold buttons) of the Lützow Free Corps, comprising mostly university students and formed during the struggle against the occupying forces of Napoleon. Whatever the true explanation, these colors soon came to be regarded as the national colors of Germany during this brief period, and especially after their reintroduction during the Weimar period, they have become synonymous with liberalism in general. The colors also appear in the medieval Reichsadler.
A very detailed historical review of the flags of Germany is available elsewhere.